description: select[k1, k2] sp select the k1'th to the k2'th elements from the given superposition indices start from 1, not 0 final element has index -1, 2nd last element -2, and so on. examples: select[2,2] split |a b c d e f g h> |b> select[4,7] split |a b c d e f g h> |d> + |e> + |f> + |g> select[2,-2] split |a b c d e f g h> |b> + |c> + |d> + |e> + |f> + |g> head (*) #=> select[1,1] |_self> tail (*) #=> select[2,-1] |_self> see also: sselect